The purpose of this research is to study the Thymus Leukemia antigens (TLa) expressed on the cell surface of mouse thymocytes and leukemic cells. The molecules with various TLa specificities will be isolated. In order to deduce the portion of the molecule(s) responsible for the specificity amino acid, lipid and carbohydrate compositions will be obtained as well as the molecular weight and subunit constitution. Provided sufficient quantities of material can be isolated the amino acid sequence of the molecule(s) will be attempted. From these studies one should be able to make deductions regarding the differences in specificities expressed on normal thymocytes versus leukemic cells. It is anticipated that such an approach will have significance in understanding normal as well as abnormal differentiation events since the expression of certain TLa specificities not only reflect the differentiation state a thymocyte is in, but certain specificities are also diagnostic of malignant transformation.